class ReconnectingWebSocket {
  constructor(url, protocols, options) {
    // Default settings
    var settings = {

      /** Whether this instance should log debug messages. */
      debug: false,

      /** Whether or not the websocket should attempt to connect immediately upon instantiation. */
      automaticOpen: true,

      /** The number of milliseconds to delay before attempting to reconnect. */
      reconnectInterval: 1000,
      /** The maximum number of milliseconds to delay a reconnection attempt. */
      maxReconnectInterval: 30000,
      /** The rate of increase of the reconnect delay. Allows reconnect attempts to back off when problems persist. */
      reconnectDecay: 1.5,

      /** The maximum time in milliseconds to wait for a connection to succeed before closing and retrying. */
      timeoutInterval: 2000,

      /** The maximum number of reconnection attempts to make. Unlimited if null. */
      maxReconnectAttempts: null,

      /** The binary type, possible values 'blob' or 'arraybuffer', default 'blob'. */
      binaryType: 'blob'
    }
    if (!options) { options = {}; }

    // Overwrite and define settings with options if they exist.
    for (var key in settings) {
      if (typeof options[key] !== 'undefined') {
        this[key] = options[key];
      } else {
        this[key] = settings[key];
      }
    }

    // These should be treated as read-only properties

    /** The URL as resolved by the constructor. This is always an absolute URL. Read only. */
    this.url = url;

    /** The number of attempted reconnects since starting, or the last successful connection. Read only. */
    this.reconnectAttempts = 0;

    /**
     * The current state of the connection.
     * Can be one of: WebSocket.CONNECTING, WebSocket.OPEN, WebSocket.CLOSING, WebSocket.CLOSED
     * Read only.
     */
    this.readyState = WebSocket.CONNECTING;

    /**
     * A string indicating the name of the sub-protocol the server selected; this will be one of
     * the strings specified in the protocols parameter when creating the WebSocket object.
     * Read only.
     */
    this.protocol = null;

    // Private state variables

    var self = this;
    var ws;
    var forcedClose = false;
    var timedOut = false;
    var eventTarget = document.createElement('div');

    // Wire up "on*" properties as event handlers

    eventTarget.addEventListener('open',       function(event) { self.onopen(event); });
    eventTarget.addEventListener('close',      function(event) { self.onclose(event); });
    eventTarget.addEventListener('connecting', function(event) { self.onconnecting(event); });
    eventTarget.addEventListener('message',    function(event) { self.onmessage(event); });
    eventTarget.addEventListener('error',      function(event) { self.onerror(event); });

    // Expose the API required by EventTarget

    this.addEventListener = eventTarget.addEventListener.bind(eventTarget);
    this.removeEventListener = eventTarget.removeEventListener.bind(eventTarget);
    this.dispatchEvent = eventTarget.dispatchEvent.bind(eventTarget);

    /**
     * This function generates an event that is compatible with standard
     * compliant browsers and IE9 - IE11
     *
     * This will prevent the error:
     * Object doesn't support this action
     *
     * http://stackoverflow.com/questions/19345392/why-arent-my-parameters-getting-passed-through-to-a-dispatched-event/19345563#19345563
     * @param s String The name that the event should use
     * @param args Object an optional object that the event will use
     */
    function generateEvent(s, args) {
      var evt = document.createEvent("CustomEvent");
      evt.initCustomEvent(s, false, false, args);
      return evt;
    };

    this.open = function (reconnectAttempt) {
      ws = new WebSocket(self.url, protocols || []);
      ws.binaryType = this.binaryType;

      if (reconnectAttempt) {
        if (this.maxReconnectAttempts && this.reconnectAttempts > this.maxReconnectAttempts) {
          return;
        }
      } else {
        eventTarget.dispatchEvent(generateEvent('connecting'));
        this.reconnectAttempts = 0;
      }

      if (self.debug || ReconnectingWebSocket.debugAll) {
        console.debug('ReconnectingWebSocket', 'attempt-connect', self.url);
      }

      var localWs = ws;
      var timeout = setTimeout(function() {
        if (self.debug || ReconnectingWebSocket.debugAll) {
          console.debug('ReconnectingWebSocket', 'connection-timeout', self.url);
        }
        timedOut = true;
        localWs.close();
        timedOut = false;
      }, self.timeoutInterval);

      ws.onopen = function(event) {
        clearTimeout(timeout);
        if (self.debug || ReconnectingWebSocket.debugAll) {
          console.debug('ReconnectingWebSocket', 'onopen', self.url);
        }
        self.protocol = ws.protocol;
        self.readyState = WebSocket.OPEN;
        self.reconnectAttempts = 0;
        var e = generateEvent('open');
        e.isReconnect = reconnectAttempt;
        reconnectAttempt = false;
        eventTarget.dispatchEvent(e);
      };

      ws.onclose = function(event) {
        clearTimeout(timeout);
        ws = null;
        if (forcedClose) {
          self.readyState = WebSocket.CLOSED;
          eventTarget.dispatchEvent(generateEvent('close'));
        } else {
          self.readyState = WebSocket.CONNECTING;
          var e = generateEvent('connecting');
          e.code = event.code;
          e.reason = event.reason;
          e.wasClean = event.wasClean;
          eventTarget.dispatchEvent(e);
          if (!reconnectAttempt && !timedOut) {
            if (self.debug || ReconnectingWebSocket.debugAll) {
              console.debug('ReconnectingWebSocket', 'onclose', self.url);
            }
            eventTarget.dispatchEvent(generateEvent('close'));
          }

          var timeout = self.reconnectInterval * Math.pow(self.reconnectDecay, self.reconnectAttempts);
          setTimeout(function() {
            self.reconnectAttempts++;
            self.open(true);
          }, timeout > self.maxReconnectInterval ? self.maxReconnectInterval : timeout);
        }
      };
      ws.onmessage = function(event) {
        if (self.debug || ReconnectingWebSocket.debugAll) {
          console.debug('ReconnectingWebSocket', 'onmessage', self.url, event.data);
        }
        var e = generateEvent('message');
        e.data = event.data;
        eventTarget.dispatchEvent(e);
      };
      ws.onerror = function(event) {
        if (self.debug || ReconnectingWebSocket.debugAll) {
          console.debug('ReconnectingWebSocket', 'onerror', self.url, event);
        }
        eventTarget.dispatchEvent(generateEvent('error'));
      };
    }

    // Whether or not to create a websocket upon instantiation
    if (this.automaticOpen == true) {
      this.open(false);
    }

    /**
     * Transmits data to the server over the WebSocket connection.
     *
     * @param data a text string, ArrayBuffer or Blob to send to the server.
     */
    this.send = function(data) {
      if (ws) {
        if (self.debug || ReconnectingWebSocket.debugAll) {
          console.debug('ReconnectingWebSocket', 'send', self.url, data);
        }
        return ws.send(data);
      } else {
        throw 'INVALID_STATE_ERR : Pausing to reconnect websocket';
      }
    };

    /**
     * Closes the WebSocket connection or connection attempt, if any.
     * If the connection is already CLOSED, this method does nothing.
     */
    this.close = function(code, reason) {
      // Default CLOSE_NORMAL code
      if (typeof code == 'undefined') {
        code = 1000;
      }
      forcedClose = true;
      if (ws) {
        ws.close(code, reason);
      }
    };

    /**
     * Additional public API method to refresh the connection if still open (close, re-open).
     * For example, if the app suspects bad data / missed heart beats, it can try to refresh.
     */
    this.refresh = function() {
      if (ws) {
        ws.close();
      }
    };
  }

  /**
   * An event listener to be called when the WebSocket connection's readyState changes to OPEN;
   * this indicates that the connection is ready to send and receive data.
   */
  onopen(event) {}
  /** An event listener to be called when the WebSocket connection's readyState changes to CLOSED. */
  onclose(event) {}
  /** An event listener to be called when a connection begins being attempted. */
  onconnecting(event) {}
  /** An event listener to be called when a message is received from the server. */
  onmessage(event) {}
  /** An event listener to be called when an error occurs. */
  onerror(event) {}
}

/**
 * Whether all instances of ReconnectingWebSocket should log debug messages.
 * Setting this to true is the equivalent of setting all instances of ReconnectingWebSocket.debug to true.
 */
ReconnectingWebSocket.debugAll = false;

ReconnectingWebSocket.CONNECTING = WebSocket.CONNECTING;
ReconnectingWebSocket.OPEN = WebSocket.OPEN;
ReconnectingWebSocket.CLOSING = WebSocket.CLOSING;
ReconnectingWebSocket.CLOSED = WebSocket.CLOSED;
